1. Field of the Invention
A spring applied parking brake system is disclosed having a main spring for normally biasing a pivot arm assembly relative to a housing toward a brake-applied position, thereby to tension the parking brake cable to apply the vehicle parking brake, and a spring compression assembly for rotating the pivot arm assembly in the opposite direction toward a brake-released position in which the tension is released from the cable. A manually-operable or solenoid-operable release device is provided for releasing a retaining assembly that normally retains the pivot arm assembly in the brake-released condition.
2. Brief Description of the Related Art
In the motor vehicle brake art, it is typical for high gross weight vehicles to use air brake mechanisms which counteract springs in the service brake system. In order to set the parking brake, the air is released to the system, thereby applying brakes at all service wheels. On the other hand, medium gross weight vehicles (i.e., trucks in the weight range of about 15,000 to 33,000 pounds gross weight) do not normally use air brakes for primary braking, thereby limiting their access to multiwheel types of parking brake systems. Owing to their weight, these heavy and medium duty vehicles normally avoid the use of pawls in their transmission systems, and consequently the transmissions do not have conventional "park" positions. In medium gross weight vehicles, a separate hydraulic brake mechanism actuated system is sometimes used to provide the parking brake function. However, not all vehicles in this environment have hydraulic systems capable of operating at the pressures and flow rates required to provide an effective parking brake function.
It is also known in the art to provide motor-driven brake systems. There also exists in the art electro/mechanical actuators for generating the loads required for parking brake systems. However, these devices often do not provide the stored energy necessary to effect the parking brake function in the event of a power failure. Furthermore, releasable helical clutch springs concentrically mounted on a shaft have been provided for retaining the parking brake in the brake-applied condition. Upon separation of the end leg portions of the spring, the turns of the spring are expanded to release the shaft, thereby to release the parking brake. Such a clutch spring could be operated manually or mechanically by such means as a solenoid.
It is further known in the art to provide parking brake systems that include a main spring normally biased in a brake-applied direction. Such systems include apparatus for compressing and holding the main spring in a brake-released position. One method of compressing the main spring is through the use of a motor driven screw drive system. Such a system is evidenced by commonly assigned U.S. Pat. No. 5,180,038 to Arnold, et al. Other systems for compressing the main spring include the use of hydraulic or pneumatic pumps and pistons. One drawback to using a screw drive system for compressing and holding the main spring is that such systems may require more time for the main spring to engage the parking brake when the retention means is released. A major drawback to using a hydraulic or pneumatic type system to compress the main spring is that the systems must remain under pressure in order to maintain the spring in the brake-released position and if the hydraulic or pneumatic systems either leak or otherwise fail, then the main spring may prematurely engage the parking brake.
The present invention was developed to overcome these and other perceived shortcomings of the prior art.